• Journal of the Korean Solar Energy Society
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• v.33 no.6
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• pp.12-18
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• 2013

Domestic solar hot water system can be divided into a passive type and an active type. In a passive type the storage tank is horizontally mounted immediately above the solar collectors. No pumping is required as the hot water naturally rises into the storage tank from the collectors through thermo-siphon flow. While, in an active type the storage tank is ground- or floor-mounted and is below the level of the collectors; a circulating pump moves water or heat transfer fluid between the storage tank and the collectors. We installed two types solar hot water systems consisting of the same storage tank and collectors at the same place, and were measured and compared typical operating characteristics under the same external conditions. In particular, the daily system performance was presented through the stirring test after the sunset. The results show that the amount of solar radiation obtained for an active type were less than a passive type on a cloudy day, because the operation of the circulation pump stops frequently took place on that day. However, on a sunny day, depending on the stable operation of the circulation pump, the amount of solar radiation obtained for an active type were increased than a passive type.

• Journal of the Korean Institute of Landscape Architecture
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• v.14 no.1
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• pp.1-13
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• 1986

The purpose of this study is to investigate the effect of temperature control by a shade tree and the lawn area. In this investigation, we find out that artificial-lawn, concerte, and exposed soil are more higher temperature than covered with plant materials. The results of the measurement may to summerized as follows; 1) Low-temperature effects of zoysia japonica is more controlled by condition of growth than leaf length of grass. Surface temperature make 0.7$^{\circ}C$ difference between long grass (15cm), and short grass (5cm), but make 5$^{\circ}C$ difference between good growth grass (230/10$\textrm{cm}^2$) and bad growth grass (80/10$\textrm{cm}^2$). 2) The surface temperature of the lawn area is 40.5$^{\circ}C$ lower on a maxinum than that of the artificial lawn (July 28, 1985). During the day of summer, shade area under the shade tree is 0.9$^{\circ}C$ lower then lawn area surface temperature, 6.9$^{\circ}C$ lower than bad growth lawn, 10.3$^{\circ}C$ lower than exposed soil, and 18$^{\circ}C$ lower than concrete surface temperature. 3) Natural irrigation effect on the surface temperature fluctuation. But this effect is changed by compositions of ground materials and time-lapse. 4) Sunny day is more effective than cloud day. 5) In summer season, surface temperature make a difference compare to temperature of 0.5-1.5m height from ground : Surface temperature is 3.4$^{\circ}C$ lower at the lawn area (11 a.m.), 4.2$^{\circ}C$ lower at the shade area the shade tree, 12.7$^{\circ}C$ higher at the concrete area (3p.m.), 38.8$^{\circ}C$ higher at the artificial lawn (2p.m.) 6) According to compositions of ground materials and season have specific vertical temperature distribution curve. 7) In summer season, temperature distribution of 0.5-1.5m hight at the shade tree is 4.8-5.7$^{\circ}C$ lower than concrete area (noon-3p.m.)

• Journal of the Korean Institute of Landscape Architecture
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• v.41 no.3
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• pp.22-30
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• 2013

This study aims to measure the thermal comfort effects of urban street trees. As the usual dry bulb air temperature does not indicate properly how the average pedestrian feels the heat of a typical summer day under the strong sunshine, we adopted the Wet Bulb Globe Temperature(WBGT). WBGT involves black globe temperature to measure the direct radiation of sun beams on our bodies, for example our heads. We measured temperatures on very sunny and hot summer days, August 3, 4, and 7, 2012, on the urban streets of Seoul, Korea. Wet bulb, globe, and dry bulb temperatures were measured under direct sunlight from 1 O'clock to 5 O'clock pm. Globe and dry bulb temperatures were measured under street tree shades nearby during the same hours. Then the WBGTs were calculated with the formulae, one for sunny outdoor spaces, and the other for shaded outdoor spaces or indoor. The results are compared with the Korean Standards Association(KS A ISO 7243). The major findings were: 1) On very sunny and hot summer days in Seoul, street tree shades lower the WBGT about 1 to 4 degrees, 2) during the hours of 3 and 4 O'clock in the afternoon, the WBGT under the tree shades are about 3 to 4 degrees lower compared to those under sunshines(approx. 29 to 32 degrees respectively), 3) This difference makes a major thermal comfort for urban pedestrians because senior citizens or weak persons are recommended to move indoor, and even healthy people are recommended stop outdoor sports and take rests in the shades when WBGT is about 32. On the other hand, if the WBGT is around 29, or 3 degrees lower, slower walking, light works or sports are allowable, 4) On site questionnaire survey confirms the thermal comforts under the tree shades, and we even could not get survey subjects on the sunny parts of the sidewalks, 5) We strongly recommend change of guidelines for urban street trees from "one row of street trees on 6m~8m intervals" to "street trees to make continuous shades".

• Korean Journal of Agricultural and Forest Meteorology
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• v.21 no.4
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• pp.358-365
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• 2019

An agrivoltaic systems (AVS) is mixed systems associating photovoltaic panels (PVPs) and crop cultivation at the same time on the given land area. It is receiving attention to improve rural economy. However, it is likely that, the crop yield should be decreased due to the reduced absorption of solar radiation by leaves. Thus, before popularizing the AVS, it is necessary to comprehend the degree of shading by PVPs in AVS. In this study, the change of radiation condition under AVS mimic shading net was investigated. The minimum and maximum of difference of photosynthetically active radiation (PAR) between under and outside shading net were 3.03 mol/㎡/day on a cloudy day and 17.08 mol/㎡/day on a sunny day. This difference decreased when the ratio of diffuse irradiance to global irradiance increased. Such a shading effect resulted in the increase of rice height and decrease of rice tillering.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.3
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• pp.222-226
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• 2012

When ship blocks are erected or pre-erected, most blocks will be at outdoors where they are not protected from weather and exposed to ray of the sun. A deck plate compared to those in radiation heat transfer from the sun will have higher temperature than it of ambient air, and will expand more than lower laying structures whose temperatures are similar with air. But deck plates and under-structures are connected, so the deck plate will be under out-of-plane deformation rather than expand in length. In this study, we considered the temperature difference between air and plate as a major parameter of out-of-plane deformation, and analyzed how much additional deformation would take place. In addition, when a deformation could take place was also analyzed based on the initial deformed shape of deck plate. Because the accuracy inspections of deck plate will be done during daytime, conventional accuracy check results on sunny day could make us feel unfair. Thus resonable datum about momentary additional out-of-plane deformation due to environmental effects have been determined. The real deformation values can be specified even under enlarged deformations by radiation-expansion.

• Journal of the Korean Society of Tobacco Science
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• v.22 no.2
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• pp.138-142
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• 2000

The effects of stalk cutting time and environmental factors such as air temperature, leaf temperature, solar radiation and leaf moisture content during harvesting and curing in burley tobacco(Nicotiana tabacum L.) on weight loss of fresh stalks and sunburning in leaves were investigated at Chonju Experiment Station, Korea Ginseng & Tobacco Research Institute in 1996 and 1997. Twelve to fifteen percent of the fresh weight was lost in 3 to 4 hours after stalk-cutting, and sunburned leaves could be observed in case of stalk cutting between 11:00 and 15:00 O'clock on a clear sunny day, when the air temperature was 34 to 35$^{\circ}C$, leaf temperature 52 to 54$^{\circ}C$, and solar radiation 700 to 940 w/$m^2$. The leaves exposed to this weather condition were sunburned within 1 hour after stalk cutting. But low temperature (below $25^{\circ}C$) with high solar radiation(above 700w/m2) or high temperature(above 3$0^{\circ}C$) with low solar radiation (below 600w$m^2$) did not induce the sunburn damage in leaves. As the leaf temperature and leaf moisture content were higher, the sunburned leaves increased. The leaves at the higher stalk position were more easily sunburned than those at the lower. This result indicates that the immature leaves with higher chlorophyll content might be more susceptible to sunburning.

• Agricultural and Biosystems Engineering
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• v.1 no.2
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• pp.73-80
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• 2000

Aerodynamics in a naturally ventilated multi-span greenhouse with plants was analyzed numerically by the computational fluid dynamics (CFD) simulation. To investigate the potential application of CFD techniques to greenhouse design and analysis, the numerical results of the CFD model were compared with the results of a steady-state mass and energy balance numerical model. Assuming the results of the mass and energy balance model as the standard, reasonably good agreement was obtained between the natural ventilation rates computed by the CFD numerical model and the mass and energy balance model. The steady-state CFD model during a sunny day showed negative errors as high as 15% in the morning and comparable positive errors in the afternoon. Such errors assumed to be due to heat storage in the floor, benches, and greenhouse structure. For a west wind of 2.5 m s$^{-1}$ , the internal nonporous shading screens that opened to the east were predicted to have a 15.6% better air exchange rate than opened to the west. It was generally predicted that the presence of nonporous internal shading screens significantly reduced natural ventilation if the horizontal opening of the screen for each span was smaller that the effective roof vent opening.

• Journal of the Korean Wood Science and Technology
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• v.18 no.4
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• pp.41-52
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• 1990

Experimental external collector type solar lumber dryer with $1.6m^2$ of collector area and $1.0m^3$ of maximum dryer capacity was designed and constructed to investigate the conditions inside and outside the dryer and collector. The efficiency of collector was calculated and numbers of drying-days and collector areas required to dry $0.2m^3$ and $1.0m^3$ of pine and oak at various an flow rate inside collector were estimated for eight cities in Korea. Average temperatures of collector-inlet and -outlet air and heat absorber were $52.5^{\circ}C$ $57.9^{\circ}C$, and $71.1^{\circ}C$. respectively at 4m/sec of an flow rate inside collector on sunny day in summer. Overall heat transfer coefficient of collector was 4.875W/$m^2^{\circ}C $ and collector efficiency was 52%. Estimated numbers of drying-days required to dry $0.2m^3$ of pine and oak from 80% to 15% moisture content at various air flow rate inside collector were 38 and 66 days. respectively. Areas of collector required to dry $1.0m^3$ of lumber at desired safe drying rate were estimated as $13.7m^2$ for pine and $16.0m^2$ for oak.

• Journal of Biosystems Engineering
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• v.32 no.2 s.121
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• pp.91-96
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• 2007

In this study, a prototype remote controlled weeder using solar module was developed and the evaluations of weeding, side walking and weeding performance were conducted to see if actual application was feasible in the paddy field. When traveling, the loss electric current was 8 to 15 A depending on operating and soil conditions. The average traveling speed was 0.25 m/s and the average slippage was 18%. When it side walked row by row, electric current consumption was 7 A on the average. When wheel rotors line went initially up and last down, electric current consumption was 12 to 15 A due to soil resistance. Electric current consumption when shifting wheel rotors line was less than 5 A due to no resistance. Field efficiency was 105 min/10a based on the test field. Operation was able to be done for 4.16 hours continually by 52 AH battery based on 300 W average maximum power consumption and 4.6 hours under sunny day considering solar module.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.1
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• pp.60-69
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• 2014

Footstep detection using seismic sensors for security is a very meaningful task, but readings can easily fluctuate due to noise in outdoor environment. We propose NSSC method based on nonlinear spectral subtraction and cross-correlation using prime footstep model signal as a footstep signal refining process that enhances the signal-to-noise ratio (SNR) and attenuates noise. After de-noising, a detection event classification method is presented as further refining process to ensure that the detection result is a footstep. To validate the proposed algorithm, representative experiments including sunny and rainy-day cases are demonstrated.